The present invention relates to an apparatus and method for inspection of tubes in a boiler. More particularly, the invention relates to an apparatus and method for guided-wave inspection of reheater tubes in a boiler.
To prevent reheater tube failures during plant operation, tubes in the reheater banks need to be inspected. If defects are determined to be large enough to cause failure, the damaged sections need to be replaced during planned outages. In a reheater, there are hundreds of tubes arranged in multiple loops in meandering fashion. Not only are the total length of tubes to inspect miles long, most of the tubes are difficult to access for inspection due to the close packed configuration of the reheater tube banks. Because of the cost and time it would take to inspect them comprehensively, the thermal power generating industries rely primarily on visual inspections and limited inspection of sampled areas on the periphery of the bundles for maintenance decisions. The reliability of a boiler reheater would be improved if the maintenance decisions were made based on more comprehensive tube condition data.
Long-range guided wave technique is a recently introduced inspection method for rapidly surveying a long length of pipe or tube for flaws from a single test position without scanning. Now widely used for examining pipelines in processing plants, this technique provides a 100% volumetric inspection of a long length of pipeline—typically more than 100 ft (30 m) in one direction—for inside and outside surface corrosion/erosion defects and circumferential cracks. In general, guided waves can detect 2% to 3% corrosion metal loss areas and circumferential cracks (here % refers to the circumferential cross-section of a flaw relative to the total pipe wall cross-section) and deep (70% through wall or larger) axial cracks. Accordingly, this technique may be useful as an inspection tool to compile comprehensive information on reheater tubes for maintenance decisions.